In conventional processing of semiconductor devices, such as fin field-effect transistor (FinFET) devices, due to finite etch selectivity between hardmask and isolation region dielectric materials, it can be difficult to recess isolation regions (e.g., shallow trench isolation (STI) regions) selective to hardmasks, especially when the recessing is performed in relatively small trenches. For example, etching of an oxide isolation region with respect to a nitride hardmask on a semiconductor fin may result in erosion of the hardmask and subsequent damage to the fin. It is important to protect fins during fin reveal processing (recessing of isolation regions) to avoid fin height variations, especially in connection with structures having dual channel (e.g., n-type and p-type) fins being simultaneously processed on the same substrate.
Heavy polymer gases have been used to increase etch selectivity of nitride films during oxide etching. However, the polymers used can block the isolation region from being recessed, especially in smaller trenches.
Accordingly, there is a need for improved methods to address the limitations in etch selectivity between hardmask and isolation region materials.